At present, the portable terminal such as a cellular mobile telephone and PDA (Personal Digital Assistant) is provided with a compact imaging device. With the widespread use of portable terminals in recent years, there has been an intense demand for high-volume production of imaging devices. To meet the users' demands for more compact and slim configuration, imaging devices are required to be smaller and less expensive.
In a recently proposed technique of producing low-cost and high-volume imaging devices, an IC chip and other electronic parts, and optical element mounted on the substrate with solder potted therein in advance are subjected to reflow processing (process of heating), and the solder is melted, whereby the electronic parts and optical element are simultaneously mounted on the substrate.
In another proposal, an aspherical and double-convex single lens characterized by low cost and high precision is used as an imaging lens to meet the demand for a more compact and less expensive imaging device.
However; mounting of components using the aforementioned reflow processing requires the electronic parts and optical element to be heated up to about 200 through 260 degrees Celsius. Then the plastic lens is deformed or discolored under such a high temperature, with the result that optical performance is deteriorated. To solve this problem, a heat resistant glass mold lens is used. This ensures the optical performance to be maintained despite exposure to high temperature during the reflow process. However, this lens is more expensive than the plastic lens, and hence, a requirement for a lower-cost imaging device cannot be satisfied.
To solve these problems, a technique has already been proposed. This technique ensures both the low cost and optical performance under high-temperature environment, using the cemented lens formed by the curing resin bonded on the surface of a glass substrate having a smaller coefficient of thermal expansion. Patent Literature 1 discloses an imaging lens using one cemented lens produced according to this technique.    Patent Literature 1: Specification, U.S. Pat. No. 3,926,380